WINDOW FUNCTION LEAD

description

LEAD() 方法用来计算当前行向后数若干行的值。

1. LEAD(expr, offset, default]) OVER (partition_by_clause order_by_clause)

example

计算第二天的收盘价对比当天收盘价的走势，即第二天收盘价比当天高还是低。

1. select stock_symbol, closing_date, closing_price,
2. case
3. (lead(closing_price,1, 0)
4. over (partition by stock_symbol order by closing_date)-closing_price) > 0
5. when true then "higher"
6. when false then "flat or lower"
7. end as "trending"
8. from stock_ticker
9. order by closing_date;

11. | stock_symbol | closing_date        | closing_price | trending      |
12. |--------------|---------------------|---------------|---------------|
13. | JDR          | 2014-09-13 00:00:00 | 12.86         | higher        |
14. | JDR          | 2014-09-14 00:00:00 | 12.89         | higher        |
15. | JDR          | 2014-09-15 00:00:00 | 12.94         | flat or lower |
16. | JDR          | 2014-09-16 00:00:00 | 12.55         | higher        |
17. | JDR          | 2014-09-17 00:00:00 | 14.03         | higher        |
18. | JDR          | 2014-09-18 00:00:00 | 14.75         | flat or lower |
19. | JDR          | 2014-09-19 00:00:00 | 13.98         | flat or lower |

keywords

1. WINDOW,FUNCTION,LEAD